THIS INVENTION relates to a plug valve, i.e. to a valve of the type in which a plug, having a passage therethrough, is mounted for rotation about an axis transverse to said passage in a body providing a passage therethrough, the plug being located intermediate the ends of the passage in the body and the arrangement being such that in one angular position of the plug about said axis the passages in the plug and in the body are in register with one another to allow the passage of fluid through the valve via said passages whilst in another position of the plug about said axis, the passages through the body and the plug are out of register with one another to prevent the flow of fluid through the valve.
Plug valves are widely used for various purposes, for example, as shut off valves for gas pipes supplying domestic or commerical premises. Since such shut off valves are, by their nature, accessible to and intended to be used by unskilled persons not under the control of the gas supply authority, it is desirable that such a valve should have no provision for adjustment or dismantling such as an unskilled person might be tempted to undertake. Furthermore, it is essential that the amount of torque required to operate the valve should be controlled within closely defined limits over the life span of the valve such that the valve cannot be operated without attachment of a suitable key to provide adequate leverage and yet such as to ensure that the valve will certainly be operable by one man after the attachment of such a key.